Low-numerical aperture confined-doped long-tapered Yb-doped silica fiber for a single-mode high-power fiber amplifier

Abstract

A low-numerical aperture (NA) confined-doped long-tapered (LCT) Yb-doped fiber is proposed and fabricated by modified chemical vapor deposition combined with solution doping technique. The LCT fiber owns the core NA of ∼0.05 and the gain dopant doping diameter ratio of ∼77%, with a core/cladding diameter of 25/400 µm at both ends and 37.5/600 µm in the middle. The laser performance is demonstrated by a bidirectional pumping all-fiber amplifier, of which a 4.18-kW single-mode (M2 factor ∼1.3) laser output is achieved with a slope efficiency of ∼82.8%. Compared with the conventional fiber, the co-pumped and counter-pumped transverse mode instability thresholds and beam quality of the LCT fiber are remarkably enhanced. Throughout the continuous operation, the LCT fiber amplifier presents high power stability with fluctuation of < 1%. These results indicate that LCT fiber has great potential in power scaling remaining excellent beam quality.

Optimization and Demonstration of Direct LD Pumped High-Power Fiber Lasers to Balance SRS and TMI Effects

“…In the aspect of fiber coiling, we found the abnormal phenomenon of increasing the TMI threshold by increasing the fiber coiling diameter [10,72]. In addition, we propose varying core diameter active fiber represented by tapered fiber, spindle-shaped fiber, and saddle-shaped fiber, which can balance SRS and TMI in the fiber and break through the power limit of conventional fiber [73][74][75][76][77][78][79][80][81]. In this work, we will focus on the optimization and demonstration of the technologies that balance the suppression of both SRS and TMI, including common methods such as fiber coiling, pump configurations, and novel methods including pump wavelength optimization and various core active fiber.…”